This invention pertains to infrared detectors. Specifically, it refers to infrared detectors whose cut-off and cut-on response spectrum can be adjusted without interference filters over a very narrow spectral bandwidth.
Photodetector response curves reach a maximum near their fundamental absorption edge and then decrease toward the shorter wavelengths. This is primarily due to surface recombination of generated photocarriers.
Previous efforts to provide narrow bandwidth have used interference filters to eliminate short wavelength radiation. The spectral response of these filters is angle of incidence dependent. This is a serious drawback as the filter has to be aimed to function effectively for radiation from a small source. Even aiming does not help if the radiation is coming from several directions.